Be more conservative about QPDF_DLL_CLASS with mingw (fixes #799)

* Define it even though previous experiments have shown it to be
  unnecessary since it seems like it may be necessary after all
* Add QPDF_DLL_CLASS to QPDFObjectHelper and QPDFDocumentHelper in
  case there's some future unknown reason why someone may want to have
  them and/or in case it helps with the weird
  QPDFNameTreeObjectHelper problem.

1 files changed, 7 insertions, 0 deletions

diff --git a/libqpdf/QPDFObjectHelper.cc b/libqpdf/QPDFObjectHelper.cc
new file mode 100644
index 00000000..3696dc03
--- /dev/null
+++ b/libqpdf/QPDFObjectHelper.cc
@@ -0,0 +1,7 @@
+#include <qpdf/QPDFObjectHelper.hh>
+
+QPDFObjectHelper::~QPDFObjectHelper()
+{
+    // Must be explicit and not inline -- see QPDF_DLL_CLASS in
+    // README-maintainer
+}